For the removal of hard materials, such as rock, ore and other extraction products in underground or overground mining, but also for the milling cutting of asphalt or concrete components in roadbuilding or building construction and the like, a multiplicity of milling systems are known which are provided with rotary-driven drums or disks, to which milling tools, such as, for example, straight shank chisels are attached in a uniform distribution. As regards disk shearer loaders used in underground mining, rock or coal is broken down by means of shearing disks which in the full cut the material to be extracted, so that about half of all the cutting tools arranged on the circumference of the drum are simultaneously in engagement with the working face. On account of the relatively long contact times between the cutting tools and the material to be broken down, the wear even of cutting tools provided with hard metal tips is high especially where hard materials to be broken down are concerned. Moreover, because of the multiplicity of individual cutting tools which are in engagement simultaneously with the material to be broken down, the pressure force remaining for each tool is relatively low, and therefore a relatively high advancing force has to be exerted on the apparatus in the direction of advance or working direction in order to break down hard materials.
In order to increase the extraction performance of apparatuses particularly for the removal of hard rock, the inventors developed apparatuses which operate by impact overlap in order to achieve a high releasing pulse for the removal of the minerals, hard rock or concrete. In the case of apparatuses operating by impact overlap, the mounting of the individual elements of the apparatus and also noise pollution sometimes present considerable problems.
Furthermore, the inventors developed the apparatus known from the previously published WO2006/079536 A1, on which the preamble of claim 1 is based and in which, even in the cutting of hard materials, long service lives of the tools can be achieved by means of reduced pressure forces. The operating principle of the apparatus known from WO2006/079536 A1 is based on arranging a plurality of tool spindles in a spindle drum or tool drum eccentrically around a drum axis in such a way that the spindle axes of the tool spindles lie parallel or, at most, at a slight inclination to the axis of rotation of the tool drum. All the tool spindles are mounted in the tool drum in such a way that the cutting tools are located, distributed on the circumference, in front of the end face of the tool drum. In operational use, a rotation of the tool drum is overlapped with a rotation of each tool spindle. What can be achieved by the overlapping of the rotational movements of the tool drum and of the tool spindles is that only relatively few cutting tools are simultaneously in operative engagement with the material to be milled or to be removed, thus resulting in a high releasing force for each individual cutting tool. In operational use, the known cutting apparatus is moved transversely with respect to the axis of rotation of the tool drum and therefore also transversely with respect to the axis of rotation of each individual tool shaft. By means of the known apparatus, excellent service lives of the tools, even in the case of hard materials and a high removal performance, are achieved. However, in the removal of the materials on closed surfaces, but also in the drilling open of core drillholes or the like, entry by virtue of a feed movement of the apparatus into the material to be removed sometimes presents problems and is sometimes impossible. Furthermore, the breakdown of materials on a large surface requires a considerable diameter of the tool drum, thus resulting in a comparatively high overall weight of the apparatus.